Geometry-driven immunomodulation in 3D-printed bioceramics: Negative curvature promotes macrophage M2 polarization via Ras-MAPK/HIF-1α signaling for vascularized osteogenesis

The geometric features of bioactive scaffolds are biophysical cues regulate cell fate, but their immunomodulatory potential in bone regeneration is yet to be determined. Growing evidence suggests that surface curvature is a potent regulator of cellular behaviours and osteogenesis. Therefore, we quantitatively decoded this underlying mechanism by identifying Gaussian curvature( K ) as a potent geometric regulator of macrophage polarization, creating a pro-regenerative microenvironment for bone repair. Using a high-throughput β-tricalcium phosphate(β-TCP) bioceramic platform ( K = −4.91 to +4.82 mm −2 ), we demonstrate that negative gaussian curvature( K − , K < −1.72 mm −2 ) promotes M2 macrophage polarization and endothelial CD31 expression. Mechanistically, single-cell transcriptomic RNA sequencing revealed that K − scaffold downregulates hypoxia-inducible factor 1-alpha (HIF-1α) via Ras-mitogen-activated protein kinase (Ras-MAPK) inhibition and thus promotes macrophage M2 polarization, consequently elevating BMP2 and VEGF secretion. In vivo , β-TCP scaffolds with K = −1.72 mm −2 achieved 42.4 % greater bone volume and higher torsional strength at 12 weeks than the scaffolds with K = +4.82 mm −2 in 15 mm critical-sized segmental defects of rabbit radius. This work indicates a quantitative geometry-immunity relationship for bioceramic scaffolds, contributing to the development of topology-mediated immunomodulatory biomaterials. Schematic of a high-throughput Gaussian curvature gradient platform for studying cell behavior, focusing on how negative Gaussian curvature drives macrophage polarization and enhances bone regeneration. • High-throughput curvature screening reveals Gaussian curvature-dependent macrophage polarization in β-TCP scaffolds. • Negative Gaussian curvature (K = −1.72 to -4.91 mm −2 ) promotes macrophage M2 polarization and CD31 expression in HUVECs. • Negative Gaussian curvature drives macrophage M2 phenotype by suppressing Ras-MAPK/HIF-1α signaling, promoting BMP2/VEGF secretion. • β-TCP scaffolds with K = −1.72 mm −2 significantly accelerated vascularized bone regeneration in critical-sized defect. • At 12 weeks post-implantation, the K = −1.72 mm −2 group achieved 83.81 % of intact native bone's torsional strength.